Our invention relates to methods of operation for numercally controlled machine tools, particularly for a machine tool capable of working on five different faces of a workpiece by comprising a spindle movable along three orthogonal axes and a worktable, for holding the workpiece thereon, that is revolvable both about its own axes and another axis set at 45 degrees to the horizontal.
Universal machine tools of standard construction can work on four faces of the work. By modifying such a machine tool to enable a 90 degree change in the direction of the spindle (or the tool mounted thereto) or of the work, there is obtained a more versatile machine capable of processing five different faces of the work. Two basic configurations have been suggested for such a machine tool, depending upon the arrangement of the axis about which the desired part is swiveled 90 degrees. One is of the ordinary table construction wherein the axis is parallel to either of three orthogonal axes. The other is of the tilting table construction wherein the axis is set at 45 degrees to two of the three orthogonal axes.
The ordinary table type affords greater simplicity in construction. Further, since the axis of rortation can be fixed anywhere between the extremities of its 90 degree angular displacement, the machine can not only work on five different faces but also perform the so called "grade machining", meaning that it can work on sloping surfaces. Offsetting these advantages is the greater bulk of the machine as the spindle (tool) or the work must travel a considerable distance with the 90 degree displacement of its axis of rotation.
The tilting table type machine tool is disclosed in, for example, British Patent Application No. 2,023,027 A. It offers the advantage of compact construction as the spindle (tool) or the work can rotate about its own tilting axis. This tilting axis, however, makes the construction of the machine very complex despite its compactness. An additional disadvantage is that, generally, and as in the case of the noted British patent application, the work has been allowed to take up only two predetermined positions, angularly spaced 90 degrees from each other, relative to the tool, there having been no fixed position in between. Thus the tilting table type machine has had no grade machining capability.